Process for treating cellulosic material with formaldehyde and sulfur dioxide

ABSTRACT

CELLULOSIC MATERIALS SUCH AS COTTON FABRICS ARE TREATED AT HIGH TEMPERATURES WITH FORMALDHYDE AND SULFUR DIOXIDE IN THE PRESENCE OF MOISTURE TO IMPROVE THEIR DIMENSIONAL STABILITY, CREASE RESISTANCE, AND SMOOTH DRYING CHARACTERISTICS.

United States Patent U.S. Cl. 8115.7 13 Claims ABSTRACT OF THEDISCLOSURE Cellulosic materials such as cotton fabrics are treated athigh temperatures with formaldehyde and sulfur dioxide in the presenceof moisture to improve their dimensional stability, crease resistance,and smooth drying characteristics.

CROSS-REFERENCE This application is a continuation-in-part of Ser. No.706,792 filed Feb. 20, 1968, and now abandoned,

BACKGROUND OF THE INVENTION In recent years various methods have beendevised for treating cellulosic fiber-containing products, such as clothmade of cotton or cotton blends, in order to impart durable creaseresistance and smooth drying characteristics thereto. For example,cellulosic materials have been crosslinked with formaldehyde, givingdurable crosslinks having good resistance to repeated laundering andalso to various acids and alkalis, and chlorine bleaches. Theseformaldehyde treated cellulosic materials are resistant to discolorationand yellowing.

However, while formaldehyde has made a significant contribution to thecotton finishing art, the results have been far from perfect. Forinstance, in some cases the formaldehyde crosslinking treatment hastended to lack reproducibility, since control of the formaldehydecrosslinking reaction heretofore has been difficult. When high curingtemperatures were used with a strong acid or a potential acid catalyst,overreaction and degradation of the cotton often occurred whichconsiderably impaired its strength. This has been notably true whenhydrogen chloride is used as the catalyst, as disclosed for instance byReinhardt et al. in U.S. Patent 3,264,054. When attempts were made toachieve reproducibility at temperatures of 50 C. or less, much longerreaction or finishing times were usually required, rendering the processeconomically relatively unattractive. This has been particularly truewhen sulfur dioxide was used as a catalyst in the previously knownprocesses such as that disclosed in British Patent 980,980, In othercases, formaldehyde crosslinking has not been able to meet commercialstandards with respect to dry wrinkle recovery. For these and similarreasons efforts have been continuing to develop new and better finishingprocesses for materials made of cellulose and particularly of cotton.

3,706,526 Patented Dec. 19, 1972 DESCRIPTION OF THE INVENTIONAccordingly, a primary object of the present invention is to provide apractical process for treating cellulosic materials with formaldehydewhich substantially prevents or alleviates the problems mentioned above.A more specific object has been to develop a process for crosslink ingcotton with the aid of formaldehyde, using a strong acid catalyst formedin the process and substantially in the amount needed, so as to keepfiber injury to a minimum.

These and other objects, as well as the scope, nature, and utilizationof the invention will become more clearly apparent from the followingmore detailed description. Unless otherwise indicated, all proportionsand percentages of materials or compounds are expressed on a weightbasis throuhgout this specification and appended claims.

In accordance with the present invention, a process is provided fortreating a cellulosic fiber-containing material to improve itsdimensional stability, crease resistance, and smooth dryingcharacteristics by treating the material with formaldehyde and gaseoussulfur dioxide in the presence of moisture at a temperature betweenabout C. and 150 C.

The process requires relatively short reaction times and gives highwrinkle recoveries while at the same time producing satisfactory tensileand tear strengths.

In the claimed invention the cellulosic material is conditioned to giveit a moisture content of between about 4 to 20 percent, preferably 5 to12 percent, based on the dry weight of cellulose fiber, and thenintroduced into a gaseous atmosphere containing a cellulose crosslinkingamount of formaldehyde and a catalytic amount of sulfur dioxide at atemperature between about 65 and about 150 C., preferably between aboutor C. and 150 C., most preferably between C. and C., for a time ofbetween about 10 seconds and 2 hours, preferably 2 to 15 or 20 minutes.In small laboratoryscale treating chambers through which a flow ofgaseous formaldehyde and sulfur dioxide is passed as described below itis desirable to have the treating atmosphere contain formaldehyde in aconcentration of, for instance, from 15 to 60 volume percent and sulfurdioxide at least at the start of the process in a concentration ofbetween, for instance, about 5 and 30 volume percent. However,obviously, very low concentrations of formaldehyde and sulfur dioxideare sufficient in equipment wherein the weight ratio of treatingatmosphere to textile material being treated is relatively high.

The optimum reaction time under any given set of other reactionconditions is one which is just long enough to effect the desired degreeof crosslinking without unnecessarily over-exposing the fabric to thereactive atmosphere. Increasing the reaction temperature or,surprisingly, increasing the moisture content of the reactive atmosphereor of the fabric permits reducing the reaction time under otherwisecomparable conditions, and vice versa. For optimum control of thecrosslinking reaction, the moisture content of the treating atmosphereis maintained between about 10 and 70 volume percent. For instance,steam may be injected at the appropriate rate into the reaction chamberfor this purpose.

The moisture content of the fabric to be treated is very important inthe process of this invention, because it is the limiting factor in thereaction between sulfur dioxide and formaldehyde to give a strong acidwhich in turn determines the extent of the crosslinking of the celluloseby reaction with formaldehyde. Initial moisture in the fabric has arelatively small effect on the amount of formaldehyde incorporated intothe fabric but will have a much larger effect on wrinkle recovery andflex abrasion characteristics. Generally speaking, too little moisturewill give low wrinkle recovery values while too much moisture causesexcessive degradation of the fabric. The amount of strong acid catalystformed in the presence of water affects the proportion of formaldehydethat actually forms crosslinks on the fabric as against that merelypresent as formaldehyde polymer, but too much exposure to acid tends toweaken the fabric by hydrolyzing the cellulose. The strong but unstableacid catalyst makes the process fast as well as easy to control in areproducible fashion.

Because of its chemical function in this process, water plays an unusualrole here in that the crosslinking reaction automatically tends to cometo a stop when water evaporates from the fabric to a point whereinsufiicient acid catalyst is formed or present to promote thecrosslinking reaction. Whereas previous formaldehyde crosslink processeswere difiicult to control, this makes the present process self-limitingin a desirable manner and produces a dry, crosslinked fabric which isessentially neutral when removed from the high temperature crosslinkingchamber, and dissipation of moisture from the hot fabric automaticallyresults in the removal of any residual catalyst therefrom. Moreover,such formaldehyde polymer as is left on the treated fabric at the end ofthe curing or crosslinking step can be easily and permanently removedtherefrom by simple heating, e.g., in air and/or steam at a temperatureabove 100 0., preferably between 110 C. and 150 C., whereby theformaldehyde polymer is depolymerized and liberation of irritatingformaldehyde from the fabric during subsequent use is precluded. Insteadof removal by heating, formaldehyde or polyformaldehyde which is notpermanently bound to the fabric may be removed and the acid catalystneutralized or extracted by washing in an otherwise conventional mannerin hot water, preferably mildly alkaline water, e.g., water whichcontains 1% sodium carbonate and/or a detergent such as a sodiumalkylbenzene sulfonate, whereupon the fabric is dried. Removal ofresidual reactants by heating is particularly advantageous in processinggarments whereas removal by washing is suitable in the continuousprocessing of flat fabric.

The fabric can be conditioned by any suitable method to give themoisture content necessary for the crosslinking reaction, such as bypadding the fabric with water and partially drying or by adjusting thefabric to an appropriate moisture content by holding it for a time at asuitable temperature and relative humidity.

Other, optional features of the invention include the addition ofvarious monomeric or polymeric additives to alter various fabriccharacteristics such as wrinkle recovery or smooth drying properties.For instance, treatment of the cloth prior to the formaldehyde-Streatment with a compound having an active hydrogen, and particularlywith a hydroxyl compound such as ethylene glycol, triethylene ortetraethylene glycol dimethyl ether, glycerine, glycidol and the like,surprisingly results in a substantially greater increase in wet wrinklerecovery than dry wrinkle recovery, and can be used for this purposewhen such an effect is desired. Other useful additives having an activehydrogen compound include amides such as urea proper or other ureas,e.g., cyclic ethyleneurea, allylurea and thiourea, acetamide, malonamideand acrylamide as well as sulfonamides such as methanesulfonamide;carbamates such as ethylcarbamate or hydroxyethylcarbamate; and so on.When such monomers which contain an active hydrogen are treated withformaldehyde in accordance with the present invention, they become fixedon the fabric so that they do not wash out. At dry add-ons of above 5%,e.g., between 5% and 20% pretreatment with the amides, and especiallywith urea, they tend to lead to unusually high tensile and tear strengthretentions. They also add crispness to the fabric after being fixedthereon by the formaldehyde.

Moreover, pretreatment of the cloth, prior to the formaldehyde-S0treatment, with polymerici resinous additives that form soft films, suchas conventional dispersions or latexes, can result in an unusually greatincremental improvement in wrinkle recovery as compared with similareffects when such additives are used in conjunction with moreconventional crosslinking treatments. Polymers can also improve the flexabrasion resistance and tear strength, or alter the ratio of dry wrinklerecovery to wet wrinkle recovery, or in some instances shorten thereaction time needed to produce an acceptable durable press fabric.Polymeric additives suitable for such purposes are, in most cases,available commercially in concentrated aqueous latex form, and it isdesirable to dilute these to a concentration of 1 to 3 percent polymerbefore padding onto the fabric. Suitable polymeric additives includesolid resinous or rubbery acrylonitrilebutadiene copolymers and mixturescontaining the same with various vinyl resins; polyethylene;deacetylated copolymers of ethylene and vinyl acetate; polyurethanes;and various polymers of alkyl acrylates, other polyesters andpolyamides. Coating of the fabrics with such polymers subsequent to theformaldehyde treatment may also be used to give similar results.

The present invention is useful for treating various natural orartificial cellulosic fibers alone or as mixtures with each other invarious proportions or as mixtures with other fibers. Such naturalcellulosic fibers include cotton, linen and hemp, and regenerated orartificial cellulosic fibers useful herein include, for example, viscoserayon and cuprammonium rayon. Other fibers which may be used in blendswith one or more of the above mentioned cellulosic fibers are, forexample, cellulose acetate, polyamides, polyesters, polyacrylonitrile,polyolefins, polyvinyl chloride, polyvinylidine chloride, and polyvinylalcohol fibers. Such blends preferably include at least 15 or 20 percentby weight, and most preferably at least 35 or 40 percent by weight, ofcotton or natural cellulose fibers.

The fabric may be knit, woven or non-woven, or be any otherwiseconstructed fabric. The fabric may be flat, creased, pleated, hemmed, orformed into virtually any desired shaped article or garment prior tocontact with the sulfur dioxide-containing atmosphere. After processing,the formed crosslinked fabric will maintain substantially the originalconfiguration for the life of the article, that is, a wash-wear ordurable press fabric will be produced.

When practicing the present invention the conditioned fabric is passedinto a reactive atmosphere containing sulfur dioxide and formaldehydewhich may be generated in any convenient manner. For instance,formaldehyde vapor may be generated by heating a suspension ofparaformaldehyde in mineral oil and the vaporized formaldehyde is thenmetered into the reaction zone along with the gaseous sulfur dioxide. Inaddition to the formaldehyde, sulfur dioxide and water vapor, thereactive atmosphere may contain inert gases such as air, nitrogen,carbon dioxide, helium, and the like. Since sulfur dioxide forms therequired strong acid catalyst by reacting with formaldehyde and water inthe process, sulfur dioxide as such need not be supplied to or presentin the process over the entire duration of the crosslinking reaction,but its supply may be discontinued after the first minute or two or whenan adequate supply of the needed catalyst has formed. Moreover, to takemaximum advantage of the self-limiting feature of this process, it canbe advantageous to pass the fabric being treated through zones ofprogressively lower humidity. Obviously, a comparable selflimitingeffect is not obtainable when the more common catalysts such as HCl,ammonium chloride or zinc nitrate are used.

To contact the fabric with the gaseous formaldehyde and sulfur dioxideany suitable means may be employed. For example, a batch systemutilizing a closed vessel or tube containing the gaseous formaldehydeand sulfur dioxide may be used in which the conditioned,moisturecontaining fabric may be placed for the appropriate time. In thealternative, a dynamic or continuous system can be used such as onewherein a stream of formaldehyde and sulfur dioxide, preferably adjustedto contain between 10 and 70 volume percent water vapor by injection ofthe required amount of steam, is passed through a closed elongatedchamber through which one also passes at an appropriate rate, eitherconcurrently or countercurrently relative to the gas, the fabric orgarments made therefrom. It is also possible to use combinations of theabove, that is, one can pass a stream of formaldehyde and sulfur dioxidegas over a stationary fabric.

DESCRIPTION OF SPECIFIC EMBODIMENTS The present invention is furtherillustrated by the following examples.

Example 1 A glass tubular reactor approximately 8 cm. in diameter and 40cm. in length, wrapped with heating tape and mounted horizontally, washeated to 120 C. Forma1dchyde was then generated by heating a suspensionof paraformaldehyde in mineral oil to between 126 C. to 132 C. and theresulting formaldehyde was fed at flow rates between 30 and 150 mL/min.into one end of the reactor. Exact measurement of the actualformaldehyde flow was difi'icult because some re-polymerization offormaldehyde took place. Sulfur dioxide was metered concurrently at aaflow rate of 24 mL/min. from a storage tank into the reactor through aninlet adjacent the formaldehyde inlet. The downstream end of the reactorwas closed with a large rubber stopper containing an exit tube 5 mm. indiameter.

A x 7.5 inch piece of conditioned cotton printcloth wrapper around asmall frame was introduced into the reactor at the downstream end of thereactor. The conditioned printcloth was bleached, unmercerized cottonprintcloth having a weight of 3.7 oz./yd. which had been padded withwater to approximately 100% wet pickup, and then partially dried at 75C. and conditioned overnight at 65% relative humidity and 70 F. to givethe fabric a moisture content of 6%. After 5 minutes in the reactor, theprintcloth was taken out, removed from the frame, rinsed with hotrunning water, washed in a household washer to which 25 ml. ofcommercial alkylbenzene sulfonate household detergent (Vel) had beencharged, and tumble dried in a household dryer.

Physical properties evaluated after one wash-dry cycle are shown inTable I.

TABLE I.VAPOR PHASE CH20/S0z TREATMENT OF COT- Formaldehyde content ofthe treated fabric was 0.8%. Formaldehyde analysis was made by weighingprintcloth samples of approximately 10 mg. to the nearest 0.1 mg. Thesamples were then heated for 30 minutes with 25 ml. of 2 N sulfuric acidat C. The solution was allowed to cool and a 2.0 ml. aliquot was pipedinto a test tube. To this aliquot was added 1.0 ml. of 0.1% aqueoussolution of chromotropic acid and 7.0 ml. of concentrated sulfuric acid.The contents of the test tube were mixed. allowed to cool, and theabsorbance at 570 m was measured with a Beckman DK-2 spectrophotometer.The amount of formaldehyde present in the printcloth was then calculatedfrom a suitable calibration curve.

It can be seen that the fabric treated according to this invention hadexcellent wrinkle recovery and crease retention when compared with theuntreated fabric.

Example 2 The cotton printcloth was treated and tested as in Example 1except that certain polymeric additives were padded onto the printclothalong with the water before conditioning and treatment. Data and resultsare given in Table II. As can be seen, the use of polymeric additives ingeneral improves wrinkle recovery values significantly.

As is evident from a comparison of the formaldehyde analyses made aftera single wash-dry cycle and after 13 such cycles, the amount offormaldehyde durably deposited in the cotton fabric in this series ofruns ranges from 0.3% upward based on the weight of the cellulosefibers. Satisfactory durable wrinkle recovery and tear strengths wereobtained in all cases.

Example 3 The printcloth was treated and tested as in Example 1 exceptthat certain monomeric additives were padded onto the printcloth beforeconditioning. Data and results are shown in Table III.

As can be seen the use of monomeric additives is capable of altering theratio of dry wrinkle recovery to wet wrinkle recovery, improving tearstrength, modifying the hand of the fabric, and so on.

TABLE II.VAPOR PHASE CHgO/SO TREATMENT WITH POLYMER ADDITIVE Pad bathcomposition Formal- Wrinkle recovery Total Reaction Moisture dehyde W+F,degrees Tear Solids, add'on, time, regain, content, strength,

Additive percent percent min. percent percent Dry Wet grams Untreatedprintcloth (control) 6.0 180 810 Properties after one wash-dry cycleNone (water only). 8.0 2 6. 3 0.5 278 302 410 Rhoplex K-14 3.2 3. 9 35.8 0 8 325 324 400 Hycar 1562 2 2. 9 3. 5 3 5. 7 0. 4 319 301 430Urethane latex, E502..... 3. 5 4. 3 3 7. 1 0.3 308 316 450 DeacetylatedElvax 210 3 1. 0 2. 3 3 6. 2 0.6 307 309 440 Properties after 13wash-dry cycles Deacetylated Elvax 210 0. 0 3 6 0 0. 4 327 311 350 1Acrylic resin. 2 Poly(butadienelacrylonitrile). 3Poly(ethylene-vinylacetate), deacetylated.

TABLE IIL-VAPOR PHASE CHzO/SOa TREATMENT WITH MONOMER ADDITIVES PRETREATPad bath composition Wrinkle recovery Total Reaction W-i-F, degrees TearSolids, add-on, time, strength, Additive percent percent min. Dry Wetgrams Untreated printcloth (control) 180 130 810 None (water only).. 1.03 289 274 390 Form amide 1. 4 264 281 460 Malonamide 7. 1 2 312 297 400Ar-Atamida 10 4. 5 3 306 296 330 Acryl amide 10 4. 7 3 290 284 340Sulfamilamide 5 6. 4 3 240 213 520 Math nnmiil fnnamide 10 5, 4 3 259269 410 2% 3. 8 3 284 270 440 10 5. 3 3 213 221 480 10 5. 4 2 254 242580 1O 6. 5 2 234 181 820 Ethylcarbamate 10 2. 3 3 289 263 360Hydroxyethylcarbamate. 10 10. 5 2 300 261 440 Ethylene glycol 10 6.0 3277 309 290 Glynerine 10 8. 9 3 280 306 300 Glyr-idnl 10 0. 8 3 215 244480 Sorhitnl 10 7. 9 3 273 277 310 Triethylene glycol dimethyl ether 102. 5 3 24.4 290 300 Tetraethylene glycol dimethyl ether 5 2. 5 3 230 283320 1 Formaldehyde plus additive after one laundering.

Example 4 The fabric was treated and tested as in Example 1, except thata 100-liter cylindrical aluminum reactor (16% in OD. x 22 /2 in. high,approximately 50 times larger than in the preceding examples) was used,the quantity of fabric heated in this set of runs was approximatelydouble that treated in the preceding examples, and a 7% aqueousdispersion of a polyacrylate was padded onto the fabric beforetreatment. The reactor walls were heated with electrical band heatersand the reactor wall temperature was controlled by an adjustablebimetallic thermostat. Steam at a certain rate was injected into thereaction zone along with the formaldehyde and sulfur dioxide in someruns, and different reaction times were used in various runs conductedin the presence of steam.

Fabrics conditioned to an initial moisture content of between 1% and 71%were treated with the formaldehyde-SO vapor mixture in this series ofruns. Fabrics having a moisture content of 6%7% prior to treatment driedalmost instantly in this large reactor, preventing formation of thestrong acid catalyst necessary for catalysing the formaldehydecrosslinking reaction. 7

In contrast, fabrics having a moisture content of 10% or more prior totreatment showed a high degree of crosslinking in the process,demonstrating that moisture content of the system dramatically affectsthe efiicacy of the crosslinking reaction and the general properties ofthe treated fabrics. Fabrics treated for 3 minutes or more at initialmoisture contents of 12% or more showed excellent wrinkle recovery butrelatively low tearing strength and abrasion resistance, indicating thatthe fabrics were maintained longer than necessary in the presence of thestrong sulfonic acid catalyst formed in the process. Fabrics having 10%moisture content showed good wrinkle recovery and relatively little lossin tearing strength and abrasion resistance when treated for 2 minutesor less. Very good results were obtained with treating times of onlyseconds, and comparable results were obtained with longer treating timeswhen the sulfur dioxide How was reduced to compensate for the longerexposure. The high rate of reaction obtainable in this process makes thelatter attractive for continuous processing.

Fabrics with moisture contents of 6%7% were treated successfully in thelarge reactor when the humidity in the reactor was increased byinjection of steam at a certain rate into the reactor, thereby avoidingrapid drying of the fabrics. Some representative data and results areshown in Table IV.

TABLE IV.-EFFECT OF HUMIDITY ON DEGREE OF CROSSLINKING Crease recoveryAs shown by Run 1 in Table IV, the formaldehydesulfur dioxide system haslittle effect when moisture in the system is low. On the other hand,when moisture of the system is increased by injection of steam asatisfactory degree of crosslinking, as indicated by the crease recoveryangle measurements, can be obtained. Comparing the results of Run 2 withthose of Run 3 it can be seen that increasing the residence time of thefabric under otherwise comparable conditions results in a higher degreeof crosslinking. Instead of achieving this increase in crosslinking byincreasing the residence time, a comparable elfect can be obtained bystill further increasing the humidity of the system.

Example 5 In this example a cotton fabric was impregnated with variousamounts of urea before exposure to formaldehyde and sulfur dioxide gasessubstantially as described earlier herein. The reactor used was similarto the one described in Example 4. The results are summarized in Table Vand illustrate the progressive improvement in the balance of strengthretained to wrinkle recovery and durable press rating gained asconcentration of urea increases. They also illustrate the superiority ofthe process, at all concentrations of urea, over a conventional durablepress process, in terms of the balance of abrasion resistance retainedto recovery and durable press rating gained.

Cotton twill fabric samples (Twist 'I will, I. P. Stevens and Company)were padded to 70% wet pickup with aqueous solutions containing 2.5% to10% urea and 2.5% (solids) Urethane Latex E-502 (Wyandotte ChemicalsCorporation), dried for 5 to 7 minutes at to C., sewn into cuifs,pressed with a commercial garment press, conditioned for a few hours inan atmosphere of 65% relative humidity, and then exposed to formaldehydeand sulfur dioxide vapors at 1.15 C. for 5 and 6 minute TABLEV.-PROPERTIES OF COTTON TWILL FAB RIOS TREATED WITH F/SO: PROCESS IN THEPRESENCE OF VARYING AMOUNTS F UREA Wrinkle recovery angle (degrees)Tearing Tensile Urea in strength Stoll flex strength Ratings 1 Exposurepad bath 2 Dry Wet (grams) abrasion, (1b.) time 1 (percent Addbn warpDurable Crease (min.) solids) (percent) Warp Fill Warp Fill Warp Fill(cycles) Warp Fill press retention Properties after 1 washing UntreatedN.A N.A. N.A 78 71 74 78 3, 800 2, 060 640 175 66 N.A N.A

Untreated washed N.A N.A. N.A. 70 68 69 72 2, 840 1,630 670 161 74 N.A.N.A.

Treated with permairesh 113 B l N.A. 150 134 144 127 1, 600 1, 080 27097 39 4. 0 3.8

l Fabrics exposed to F/SOz (formaldehyde-sulfur dioxide) vapors at 115C.

2 All pad bath solutions contained 2.5% solids Urethane Latex E-502.

3 Fabric specimens tore across filling yarns only. I Greased fabricspecimens rated after tumble drying. 5 Conventional durable pressprocedure.

NoTE.-N.A.=Not applicable.

periods. For comparison, other fabric samples were padded with anaqueous solution containing 5% solids of Permafresh 113B(dimethyloldihydroxyethyleneurea, Sun Chemical Company) and 2.5 solidsof Urethane Latex E- 502. Wet pickup, drying, sewing, and pressingconditions were the same as above. These samples were conventionallyheat-cured for 7.5 minutes at 160 C.

Intermediate concentrations of urea enhanced the wrinkle recovery anglesobtained, a trend which was reversed at the highest level of ureaconcentration. Although it is simplest to make comparisons betweentreatments when they result in identical levels of wrinkle recovery, thevariations obtained were not great enough to invalidate the followingconclusions.

Increasing the concentration of urea used progressively improved thebalance of tensile and tear strength to wrinkle recovery and durablepress rating. In round figures, use of urea in the bath improved thetear and tensile strength values of formaldehyde and sulfur dioxidetreated fabric by 40%, or on the basis of untreated values, withoutsacrifice of wrinkle recovery or durable press rating. There was nosignificant change in Stoll flex abrasion resistance. The conventionaldurable press treatment gave lower Stoll flex abrasion resistancefigures than any level of urea concentration, and comparable tensile andtear strength figures to the zero urea concentration level, allcomparisons being made at comparable levels of wrinkle recovery anddurable press rating.

In still other examples, which are not reported here in detail, thefabric samples were similarly treated using various concentrations ofcyclic ethyleneurea and trimethylolmelamine, respectively, in the padbath instead of urea proper. Similar results were obtained.

While all of the above examples were conducted at atmospheric pressure,subor superatmospheric pressures may be used but are not necessary.

The principles, preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.However, the invention which is intended to be protected herein may bepracticed otherwise than is described without departing from the scopeof the appended claims.

What is claimed is:

1. A process for improving the dimensional stability, wrinkle resistanceand smooth drying characteristics of a cellulose fiber-containing fabricwhich comprises:

(a) conditioning the fabric to give the cellulose fibers a moisturecontent of between about 4 and 20% based on dry weight of cellulose;

(b) thereafter heating the conditioned moisture-containing fabric in areactive vapor atmosphere containing effective amounts of formaldehyde,water vapor and catalyst-forming sulfur dioxide to a temperature betweenabout 65 and 150 C. for a time of between about 10 seconds and 2 hoursuntil formaldehyde in an amount equal to at least 0.3% by weight of saidcellulose fibers is durably deposited in the fabric and the cellulosefibers become effectively crosslinked, said heating being conductedwhile governing the amount of water vapor in said atmosphere to controlthe amount of moisture in said fabric and thereby regulate the amount ofstrong acid catalyst formed by the reaction of formaldehyde and sulfurdioxide, a reaction in which water is the limiting factor, to provide aself-limiting reaction system; and

(c) heating the thus crosslinked fabric to dissipate water vapor,residual catalyst and unbound formaldehyde therefrom, thereby directlyproducing a dry, crosslinked, essentially neutral fabric.

2. A process according to claim 1 wherein the fabric is one containingat least 35% of cotton fibers by weight.

3. A process according to claim 1 wherein the fabric is heated in thereactive atmosphere in step (b) to a temperature between about and 150C. for a time of between about 2 and 20 minutes and is heated in step(c) to a temperature above C.

4. A process according to claim 3 wherein the fabric is introduced intothe process after having been formed into an article of predeterminedconfiguration.

5. A process according to claim 3 wherein the fabric is acotton-polyester blend containing at least 35% cotton by weight and isintroduced into the process after having been formed into an article ofpredetermined configuration.

6. A process according to claim 3 wherein the fabric is padded in anaqueous solution of urea and contains from 5 to 25% dry add-on of ureaprior to exposure to formaldehyde and sulfur dioxide.

7. A process for improving the dimensional stability, crease retentionand smooth drying characteristics of a cellulose fiber-containing fabricwhich comprises:

(a) conditioning the fabric to give the cellulose fibers a moisturecontent of between about 4 and 20% based on dry weight of cellulose;

(b) thereafter heating the conditioned moisture-containing fabric in areactive vapor atmosphere containing an effective amount offormaldehyde, water vapor and catalyst-forming sulfur dioxide to atemperature between about 65 and 150 C. for a time of between about 10seconds and 2 hours until formaldehyde in an amount equal to at least0.3% by weight of said cellulose fibers is durably fixed in the fabricand the cellulose fibers become effectively crosslinked, said heatingbeing conducted while governing the amount of water vapor in saidatmosphere to control the amount of moisture in said fabric and therebyregulate the amount of strong acid catalyst formed by the reaction offormaldehyde and sulfur dioxide, 3. reaction in which water is thelimiting factor, to provide a self-limiting reaction system;

(c) washing the thus crosslinked fabric in water to remove residualcatalyst and impermanently bound formaldehyde therefrom; and

(d) drying the washed, crosslinked fabric.

8. A process according to claim 7 which process is continuous andwherein the fabric being treated is fiat fabric.

9. A process according to claim 7 wherein the fabric is acotton-polyester blend containing at least 35% by weight of cotton.

10. A process for improving the dimensional stability, wrinkleresistance and smooth drying characteristics of cotton-containingfabrics which comprises:

(a) conditioning the fabric to give the cotton a moisture content ofbetween about 4 to 20% based on dry weight of cotton;

(b) exposing the conditioned fabric to a reactive vapor phase containingwater vapor, about 15 to 60 volume percent formaldehyde and at leastinitially from about 5 to 30 volume percent sulfur dioxide in a reactionzone maintained at a temperature between about 90 and 120 C. for a timeof from about 2 to 20 minutes, thereby effecting the desired degree ofcrosslinking; and

(c) at the end of said crosslinking step (b) removing residual catalystand unbound formaldehyde from the fabric by heating it in an inertgaseous atmosphere, thereby directly producing a dry, crosslinked,essentially neutral fabric.

11. A process according to claim 10 wherein steam is injected into thereaction zone in step (b) to adjust the water vapor concentrationtherein at between about 10 and percent and thereby to retardevaporation of moisture from the conditioned fabric and control thecrosslinking reaction.

12. A process according to claim 10 wherein the fabric is treated priorto the formaldehyde crosslinking step with a compound containing anactive hydrogen and selected from the groups consisting of polyhydricalcohols, ureas, amides and carbamates.

13. A process according to claim 10 wherein the fabric is introducedinto the process after having been formed into an article having apredetermined configuration.

References Cited UNITED STATES PATENTS 2,441,859 5/1948 Weisberg et al8116.4 3,264,054 8/1966 Reinhardt et a1. 8116.4 3,310,363 3/ 1967Russell et al. 8-116.4 3,660,013 5/1972 Payet et a1. 8116.4

FOREIGN PATENTS 980,980 1/ 1965 Great Britain 8-1164 OTHER REFERENCESGuthrie: American Dyestulf Reporter, vol. 51, No. 14,

Gagliardi et al.: Textile Research Journal, vol. 36, pp. 168-177 (1966).

Mehta et al.: Journal of the Textile Institute, vol. 58, pp. 279-292(1967).

GEORGE F. LESMES, Primary Examiner J. CANNON, Assistant Examiner US. Cl.X.R.

2243; 8-115.5, 115. 6, 116.2, 116.3, 116.4, 129, 149.1, 149.2, 149.3,DIG. 4, DIG. 9, DIG. 10, DIG. 21; 34-37; 38-144

